Process for making resilient porous products



\ July 18, 1944. R; G. CHOLLAR PROCESS FOR MAKING RESILIENT POROUS PRODUCTS Filed Jan. 19, 1942 FIG. 1

v 'cpMMmuTe-n V UNVULCIINIZED RUBBER SOLUBLE FILLER FIG. 4

\ nzwwxcmm Robert G. Chollir 1 Inventor By aux/@206 His Attorney Patented July 18, 1944 UNITED STATES PATENT OFFICE PROCESS FOR MAKING RESILIENT POROUS PRODUCTS Robert G. Chollar, Dayton, Ohio, assignor to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Application January 19, 1942, Serial No. 427,326

Claims;

the printing characters in relief thereon or in.

intaglio therein, the product is eminently suitable for other uses where micro-porous material of uniform pore size and having rubber-like qualities is required, such as, for instance, for filtering webs, for resilient porous partitions, for liquid passing separators more or less electrically and chemically inert, for wicks, or for porous fabricating material.

The process disclosed herein being directed principally to the making of printing plates or inking webs, the preferred rubber-like materials specified are the oil resisting butadiene co-polymers, which are chosen because of their resistance to attack by ink, particularly dye inks containing oily substances, but the invention is not to be deemed restricted to such particular materials, as

other materials of a rubber-like nature having different characteristics may be used in accordance with the use to which the porous product is put.

Therefore, it is the principal object of this invention to provide a process for themaking of micro-porous rubber-like webs having interconnecting pores.

Another object of the invention is to provide a process for the making of micro-porous resilient webs.

Another object of the invention is to provide a process for the making of micro-porous resilient printing plates.

Another object of the invention is to provide a micro-porous rubber-like printing plate resistant to corrosion or distortion by printing inks containing oily substances.

Another object of the invention is to provide a rubber-like printing plate having microscopic pores therein which constitute approximately 45% or more, by volume, of the plate as a whole.

With these and incidental objects in view, the invention includes certain novel features, the essential elements of which are set forth in the preferred embodiment to be described in conjunction with the drawing and in appended claims.

In the drawing:

Fig. 1 shows the mixing of the comminuted ingredients.

Fig. 2 shows the mixed ingredients in a molding die.

Fig. 3 shows the molding die in position in a steam-heated press.

Fig. 4 shows the molded and vulcanized article before removal of the filler.

Fig. 5 shows a method of washing out the filler.

Fig. 6 shows an enlarged fragment of the porous rubber web.

10 General description The process consists essentially of the'step of intermlingling intimately certain proportions of vulcanizable comminuted rubber-like material with an equally comminuted filler substance in certain proportions; the step of molding the material under pressure; the step of vulcanizing the molded product either in the mold or after it has been released from the mold; and the step of removing the filler from the molded product, leaving interconnecting pores which the filler formerly occupied. In general, it may be said that the proportion of the rubber-like substance to the filler should be about 55% by volume of the rubher-like substance to about by volume of the filler substance. The proportions mentioned assure a bonding of the rubber-like material in molding, yet leave the spaces, which were occupied by the filler before it is removed, intercon- 40 necting. The filler is of such a material that it may be removed by means which will not destroy the rubber-like part of the molded structure.

The molding step- {5 In the preferred embodiment, a synthetic rubber, of the type of the butadiene co-polymers, containing standard vulcanizing ingredients, is comminuted so that the particles are uniformly more or less of a size, which size may be selected from a range of particle sizes between those that with a filler ll of preferably the same or smaller particle size, which filler is inert to the rubberlike material, dry, non-volatile under pressure and vulcanizing heat, and practically incompressible. It is to be noted that the filler may be compounded with the rubber and the compounded mass comminuted instead of comminuting the rubber-like material and the tiller separately, although such compounding, by coating the filler particles with rubber, prevents a complete removal of the filler. The filler must be removable by means that does not adversely aifect the rubber after it has been molded.

The preferred filler for the butadiene co-polymers is sodium nitrate, but other fillers which are easily removable from the molded product by dissolving them'out by liquids inert to the rubberlike material may be used, suggested substances being sodium carbonate, ammonium sulphate, zinc, and poly-vinyl alcohol. The list of materials given for fillers is not to be deemed exhaustive. Some of the named materials such as zinc, the carbonates, and the nitrates may be dissolved out of'the molded product by hydrochloric acid or dilute nitric acid. The sodium nitrate may also be dissolved out of the molded product with hot water, preferably having contained therein a wetting agent such as one of the soaps, or one of the sulfonated fatty' alcohols, or salts of the aliphatic penetrates. The materials, after being intimately mixed, are placed in a die mold l2 (Fig. 2), preferably of the positive pressure type, in a layer l3 of from 91000 of an inch in thickness to of an inch in thickness, depending upon the mesh size of the ingredients. The finer the mesh size of the ingredients used, the more difllcult it is for the filler solvents to penetrate through the entire molded web. For a 325 mesh mix, for instance, of 'an inch will be the maximum thickness of a web from which the flller I can be readily dissolved by washing, whereas the coarser 100 mesh mix web may be of an inch thick. Thicker webs may be cleared of filler by washing and manipulating the piece, thus working the filler out and the solvent in.

If the product is to be av printing plate, the mold may be supplied with a suitable matrix. For making any other surface configuration, or for making a web of other than a plane configuration, ordinary molding practices are followed. A pressure. of from 250 pounds to over 6,000 pounds per square inch may be used (Fig. 3). A vulcanizing temperature of approximately 307 degrees Fahrenheit for the butadiene ard vulcanizing temperature for any other of the rubber-like materials that may be used, may be applied during the molding in a press I, as shown in Fig. 3, by steam supplied to the press through pipes 15, after the molding, or after the removal of the molded product from the mold. The matrix placed in the die may be Bakelite or other incompressible substance inert to the pressure and heat used.

of sodium nitrate co-polymers, or a stand- I claims which follow.

What is claimed is:

1. -The process of making a microscopically porous web, including the step of intermingling finely comminuted moldable resilient material with a comminuted non-resilient soluble filler; the step of molding the mingled substances under pressure into a web; and the step of removing the filler by dissolving it in a solvent to which the resilient material is relatively inert.

2. The process filler by a solvent not aifecting the rubber-like material by temporary contact therewith.

process of making a micro-porous rub- 4. The process of making a micro-porous web, including the step of comminuting, to a uniform particle size somewhere between 25 and 325 mesh removed.

5. The process of making a'micro-porous rubber product, including the step of comminut- 45 parts by volume of the filler; the step of molding said intermingled substances under pressure between 250 and 6000 pounds to the square inch; the step of vulcanizing the molded product in the mold or after removal from the mold; and the step of washing the filler out with a dissolving agent that is inert as to the rubber.

6. The method of making a resilient porous product, including the step of comminuting a vulcanizable butadiene co-polymer to a uniform particle size somewhere between 25 mesh and 325 mesh to the inch; the step of comminuting a filler substance having the characteristics of relative incompressibility, of chemical inertness to the butadiene co-polymer, and of remaining dry and non-volatile under heat and pressure, to the same mesh size or smaller than the mesh size of the butadiene co-polymer; the step of intimately intermingling approximately 55% by volume of the butadiene oo-polymer with 45% by volume of the filler; the step of molding the intermingled substances to the desired form under pressure somewhere between 250 pounds to the square inch and 6000 pounds to the square inch; the step of vulcanizing the molded product either while under pressure in the mold or after said molded product has been removed from the mold; and the step of dissolving out the filler from the molded product by a solvent which is inert to the butadiene co-polymer by washing.

7. A process for making a micro-porous resilient web, including the step of comminuting vulcanizable rubber or rubber-like material to a uniform particle size somewhere between 25 mesh and 325 mesh to the inch; the step of comminuting a dry, pressure-resisting, non-volatile, and non-compressible substance to a particle size at least as small as the particle size of the rubber or rubber-like material; the step of intimately intermingling to a uniform condition 55% of the comminuted rubber or rubber-like material by volume with 45% or the filler material by volume;

size, including the step of molding a mixture of moldable rubber of micro-fine particle size with a filler of particle size at least as time as the rubber; and the step of dissolving out the filler from the molded product by a solvent inert as/to the rubber.

9. A process for making micro-porous rubber having the pores interconnecting and of uniform size, including the step of molding a mixture of vulcanizable moldable rubber of microfine particle size with a filler of particle size at least as fine as the rubber; the step of vulcanizing the molded body; and the step of dissolving out the filler from the molded product by a solvent inert as to the rubber. v

10. A process for making a micro-porous butadiene co-polymer having the pores interconnecting and of uniform size, including the step of molding a mixture of moldable resilient butadiene co-polymer of micro-fine particle size with a filler of particle size at least as fine as the butadiene co-polymer; and the step of dissolving out the filler from the molded product by a solvent inert as to the butadiene co-polymer.

ROBERT G. CHOLLAR. 

